1. Field of the Invention
This invention relates to imaging materials comprising certain Te(II) complexes containing both a tellurium atom and a Pb, Sn, Ge or Si atom. In one aspect it relates to a photographic material comprising the described Te(II) complexes, such as a photothermographic material containing a combination of (a) a photosensitive metal salt with (b) an image-forming combination containing the described Te(II) complex and other components.
In another aspect it relates to a process of developing an image in a heat-developable photographic material containing the described tellurium complex. A further aspect of the invention relates to a heat-developable imaging material containing certain physically developable nuclei and an oxidation-reduction image-forming combination containing the described Te(II) complex. Another aspect of the invention relates to certain novel Te(II) complexes containing a Pb, Sn, Ge or Si atom and processes of preparing the described complexes.
2. Description of the State of the Art
It is known to provide an image in an imaging material containing certain metal complexes, such as certain tellurium complexes. These materials can be useful in what are described as photographic materials for dry processing with heat. These imaging materials are sometimes described as heat developable photographic materials or photothermographic materials. Such heat developable photographic materials after imagewise exposure to provide a developable latent image are heated to provide a developed image in the absence of processing solutions or baths.
It has been desirable to provide reduced silver concentrations in photosensitive silver materials, especially heat developable silver imaging materials. Attempts have been made in the past to provide this desired reduced silver concentration. For example, U.S. Pat. No. 3,152,903 of Shepard et al, issued Oct. 13, 1964 describes an imaging material containing a non-silver component such as titanium dioxide or zinc oxide. It is indicated that the image-forming composition can comprise a latent irreversible oxidation-reduction reaction combination which is capable of initiation by electron transfer from a non-silver photocatalyst. The photocatalyst can be, for example, zinc oxide or titanium dioxide. A disadvantage of the imaging material described in this patent is that no image amplification is possible. This provides the necessary requirement of undesirably high concentrations of non-silver materials. It has been desirable to overcome this problem by providing a more effective non-silver heat developable material, that is a material which enables desired latent image amplification.
An image amplification step is an important factor in photographic materials having increased speed. In increased speed materials, a latent image is generally formed by imagewise exposure of the photosensitive material to suitable radiation. The resulting invisible or latent image formed is then used to catalyze the reduction of a material in a high oxidation state to a visible image in a low oxidation state. In silver halide photographic materials, for example, exposure of photographic silver halide to light results in formation of silver nuclei which then can catalyze the further reduction of silver halide to silver in the presence of a reducing agent.
The use of tellurium materials in imaging is known. For instance, it is known to produce tellurium imaging by disproportionation of tellurium dihalides. Imaging materials are known in which images are formed by disproportionation of certain metal compounds such as tellrium halides. The images are formed in the presence of a processing liquid or solution which aids in the disproportionation reaction. The unexposed dihalides, however, are dark in color causing poor image discrimination. The tellurium dihalides are typically unstable in air and undergo light induced decomposition only when moistened with an organic solvent. This is a disadvantage in most imaging materials, especially those designed for processing in the absence of solutions or baths.
Other tellurium imaging materials include those which are certain Te(IV) compounds wherein the tellurium is bonded directly to a carbon atom. These tellurium materials undergo what can be described as a unit quantum photoreduction to yield a tellurium image. The materials and imaging process do not involve a catalytic amplification of a latent image. That is, the tellurium (O) formed upon exposure does not catalyze the decomposition of other components or other reaction of the Te(IV) compounds. The process and imaging material are inherently photographically slow in speed and limited in usefulness because they do not enable an amplification reaction.
An imaging combination comprising (1) a tellurium complex as an oxidizing agent with (2) a reducing agent is known to provide an amplified image in certain imaging combinations is described in U.S. Application Ser. No. 703,477 of Lelental and Gysling, filed July 8, 1976, now abandoned and related to U.S. 4,144,062 and U.S. 4,152,155. This imaging combination can be useful in heat developable photographic materials containing, for example, photographic silver halide or other sources of developable nuclei. The tellurium complexes, however, do not involve metallic atoms other than tellurium atoms. It has been found that the inclusion of other metal atoms in the tellurium complex provides an added source of imaging metal.
Tellurium compounds and complexes have been proposed for other purposes including other imaging materials. While these materials include tellurium compounds and complexes, none involve the formation of an image with a tellurium complex containing other than a tellurium atom as a source of metal for imaging.
Tellurium complexes are known which contain not only a tellurium atom but also an atom of some other metal, such as Si, Ge, Sn or Pb. These are described, for instance, in the following publications: (1) "The Organic Chemistry of Tellurium", by Kurt J. Irgolic, Gordon N. Breach Science Publishers, 1974, such as on pages 247-254; and (2) Zhurnal Obschchei Khimii, Volume 37, No. 5, pages 1037-1040, May, 1967. The latter publication describes, for instance, the tellurium compounds or complexes: (a) (C.sub.2 H.sub.5).sub.3 MTeC.sub.2 H.sub.5 and (b) (C.sub.2 H.sub.5).sub.3 MTeSn(C.sub.2 H.sub.5).sub.3 wherein M is Si or Ge. Also, none describe a process which enables the formation of the described tellurium materials that eliminates the need for a multistep process and the need for purification before using the tellurium compound or complex in an imaging material, such as a photothermographic material.
Materials are known in the imaging art in which metal nuclei are used for physical development purposes. None of these materials, however, involve nuclei in a heat developable photosensitive material containing a tellurium compound or complex which contains, in addition to the tellurium atom, an atom of, for example, germanium, tin, lead or silicon.
There has been a continuing need to provide improved tellurium imaging materials and processes. This continuing need has been especially true for heat developable photosensitive materials which enable amplification of a nuclei image. There has also been a need to provide improved tellurium complexes which contain the described non-tellurium metal atoms and to provide improved processes which eliminate the need for preparing the described tellurium complexes in multiple steps.